Timing drives generally comprise either an oil-lubricated chain or a toothed belt running in a dry condition. A timing drive running in contact with oil has recently been made comprising a toothed belt made so as to withstand the chemical attack of oil and to have a lifespan equal to 240000 km and 10 years in a motorcar and to 350000 km and 10 years in a light commercial vehicle.
A belt drive for use in contact with oil is lighter and causes less vibrations with respect to a chain drive. Furthermore, experimental tests have demonstrated that such drive allows to reduce consumptions with respect to a traditional chain drive.
Such advantages may now be obtained also by upgrading or retrofitting engines originally designed for a chain drive with such a belt drive. However, a chain drive presents different dimensions with respect to those of a belt drive. Therefore, in order to upgrade a chain drive to a belt drive, all the components of the latter must be fitted within vanes originally designed for the chain drive. Possibly, some non-substantial parts of the engine may be modified in a marginal manner.
In particular, a belt drive comprises an automatic tensioner and such device appears particularly critical for the assembly within a vane originally designed for a chain drive.
International patent application WO-A1-2006111988 filed by the same applicant describes a tensioner for an application in contact with oil comprising a fixed pin, a disc mounted in an eccentric manner on the pin and actuated by a tensioning spring and a pulley mounted in a concentric manner on the disc by means of a ball bearing. Furthermore, the tensioner comprises a friction damping device to appropriately dampen the oscillations of the belt also in the presence of oil.
Such tensioner is compact in the axial direction but presents relatively high dimensions along the radial direction and therefore cannot be used when the accommodation compartment for the drive presents a particularly complex geometry.